The present invention relates generally to pulpwood grinders. Specifically, the present invention relates to a blocking slab suitable for use in such grinders.
When grinding wood in a pulpwood grinder for making pulp, or the like, wood is placed in a grinding chamber and pressed against a rotating grindstone. Essentially, the wood is ground into fibers which are passed from the grinding chamber through gaps between the walls of the grinding chamber and the grindstone. Unfortunately, shims (wood chips) and shives (splinters) also pass through the gaps. The shims and shives create a host of problems in the paper making process. For example, shims and shives can block the grinder or the piping. Also, shims and shives in pulp create an inferior product.
The pulpwood industry has, for many years, faced the problems caused by permitting shims and shives to pass with the pulp. Despite the recognition of such problems, however, the techniques used within the industry to eliminate shims and shives from the pulp have been heretofore less than successful.
For example, one attempted solution is to screen the pulp to eliminate the shims and shives. However, screening the pulp introduces inefficiencies in the pulp making process because it impedes the flow of pulp. Screening also requires an attendant and thus results in added labor and costs.
Certain types of finger bars have also been used. Finger bars with a series of rake-like fingers are shown in U.S. Pat. No. 3,734,419. Such finger bars have been secured closely spaced apart from the grindstone in the gap. Such finger bars do not adequately impede the passage of shims or shives. Thus, the pulpwood industry has long considered finger bars inadequate.
Blocking slabs with long narrow strips placed in the gap proximate the grindstone and parallel to the axis of the grindstone have also been tried, but are less than adequate. U.S. Pat. No. 4,595,150 shows a typical blocking slab having a series of longitudinally-oriented, spaced-apart ribs parallel to the axis of the grindstone. The ribs form a series of recesses therebetween and parallel to the axis of the grindstone.
During use, the recesses of the typical blocking slab quickly become packed full of shims, shives and pulp which creates a seal between the blocking slab and the grindstone. Blocking slabs consequently impede the passage of pulp through the gap and significantly reduce pulp making efficiency. The grinder is required to expend more energy to pass pulp through the seal. Further, downtime can result when the grinder is stopped to clear the seal formed in the recesses.